Manufacture of boron nitride



United States Patent MANUFACTURE OF BORON NITRIDE Frank H. May and Vladimir V. Levasheli, Whittier, Califi, assignors to American Potash & Chemical Corporation, a corporation of Delaware No Drawing. Application June 22, 1955 Serial No. 517,352

9 Claims. (Cl. 23191) 'having the following average analysis:

Percent B 27-32 N 26-34 H 2.5-3.0 C 0.7-1.0 O (diii) 43.8-30.0

If the solid material so produced is thereafter maintained in an ammonia atmosphere at an elevated temperature of 850 C. and higher, it is converted into boron nitride, the conversion being attended usually by a 25- 35% loss in weight but without any loss in boron.

We have further found that composition of the heat stable white solid material obtained depends to a great extent on the velocities at which the reactants are allowed to pass through the hot zone, as well as the furnace temperature. Thus, the lower the feed rate of the reactants, at a given furnace temperature of above 850 C., the higher is the boron and nitrogen content of the resultant white, heat stable, solid material.

The practice of the invention will become further apparent from a consideration of the following typical preparations of a heat stable, white solid material having an average boron content of 27-32% and an average nitrogen content of 26-34%.

A tube furnace was heated to about 900 C. while being swept out with ammonia gas. Methyl borate was then introduced into the hot zone at a rate such that a small excess of ammonia over the 1/1 mole ratio of NH to (CH O) B was maintained in the hot reaction Zone. An excess of ammonia is a necessary feature of the process for it ensures formation of the white solid material, without any undesirable decomposition. Carbonaceous substances are formed in the hot reaction zone whenever an excess of methyl borate is present. The finely dispersed white solid material, a major porton of which is swept out of the hot reaction zone by the efiluent gas stream, is collected by settling out in a suitable container.

The white product of the gaseous reaction is converted to boron nitride with an accompanying 25-35% weight loss by holding the material in the presence of ammonia and at an elevated temperature above 850 C.

The following are examples of the preparation of the heat stable, finely dispersed white solid material, having an average boron content of 27-32% and an average nitrogen content of 26-34%:

Example I.80 grams of methyl borate were fed into 2,824,787 Patented Feb. 25, 1958 ICC an ammonia-swept furnace at about 900 C. over a period of four hours. 6.5 grams of white solid material were recovered from the trap system. An additional 12.8

grams were recovered from the tube furnace. On the basis of boron recovery, as determined by analysis of the products, a 69.3% yield of white solid material was obtained.

Example II.106 grams of methyl borate were fed at the rate of 19 grams per hour into a 900 C. furnace swept with ammonia at the rate of 14-18 grams per hour. 14.0 grams of white solid material were collected from the trap system and an additional 12.0 grams were recovered from the furnace. On the basis of boron obtained, the yield was 71.4%.

Example III.-180 grams of methyl borate were fed at 45 grams per hour into a 950 C. furnace swept with ammonia at the rate of 90 grams per hour. 30.2 grams of white solid material were collected from the trap system and an additional 20.5 grams were recovered from the furnace. On the basis of boron obtained, the yield was 71.1%.

Example 1V.229 grams of methyl borate were fed at the rate of 101.8 grams per hour into a 1050 C. furnace swept with ammonia at the rate of 140 grams per hour. 39 grams of white solid material were collected from the trap system and an additional 29 grams were recovered from the furnace. On the basis of boron obtained, the yield was 75.0%.

The results of the above are summarized in Table 1: TABLE 1 Preparation of heat-stable white solid from methyl borate and ammonia Example No I I II III I IV Furnace Temperature, C 900 900 900 1050 Starting material, (OH3O);B, grams 80 106 180 229 Percent B 10. 41 10. 41 10. 41 10. 41 White product, grams. 19. 3 26.0 50. 7 68 Percent B 29. 9 30. 3 26. 3 26. 3 Percent Yield (boron recovery) 69. 3 71. 4 71. 1 75.0

TABLE 2 Heat treatment in NI-I atmosphere Product Anal sis B Retention Time, Temp., Loss in y N iiilr l e Hours C. Wt. Percent Percent Percent 0210.

B N from N) vapor phase methyl borate-ammonia reaction-at 500C; furnace temperature, a compact white crystalline material is obtained having the following analysis:

7 Percent B 9.35 N 10.75 H 6.2 .C 17.2

0 (diff.) 56.50

This material is quite differentvfrom theflutfy, white,

7 heat stable solid produced at furnace temperatures of the'order of "850 C. Further,.heat treatment at 850 C. orjhigher in an ammonia atmosphere of the 500 C. V white crystalline product resultsain its .sublimationfrom 7 -the reaction zone without apparent alteration.

In another test of the vapor phase methyl borate-ammonia reaction, at-about.750 C. furnace temperature, a

mixture'of the heat stable, white',;finely dispersedsolid and of the. compact crystalline material was obtained.

This mixture had the following average composition;

Percent 18.35 14.1 5.0 4.7 .O (difi.)' 57.35

When this mixture was held at .a temperature. above 850 C.v in an ammonia atmosphere, there occurred partial decomposition, as indicated by a darkening of color of the product, partialsublimation and .a 55% loss in weight, as compared to the 25-35% loss in weight obtained during the heat treatment of material from the ,above 850 C. furnace temperature runs.

Instead of methyl borate, one can use any other borate ester, the reaction being as follows: j a

,where ROH'is any alcohol. The following examples further illustrate the practice of this invention. Example V.A quantity of 22 grams of ethyl borat was fed at 25 grams per hour into a 950 C. tube furnace swept with ammonia at the rate of. 115 'grams/houn.

A quantity of brownish colored solid material was collected from the trap system and the tube furnace. Infrared spectrum analysis of the solids produced a curve essen- V '4 7 reaction at'a temperature above about 800 C. to produce boron nitride.

3. In a process for producing boron nitride the steps of producing a boron complex comprising reacting ammonia with ethyl borate at a temperature above about 850 C., the 'ammoniabeing. present in at least a slight excessover amoleto mole ratio. with. ethyl borate, and recovering the product of reaction.

4. In a process fforproducingboron; nitride, the steps,

of producing a boron complex .comprisingreacting am monia'and a lower alkyl borateester at a 'temperature above about 850 C.,.the. .ammonia'being present in at least a slight excess over a mole" to mole ratio with the borate ester, and recovering the product of reaction.

a 5; A process forproducing boron nitride, the steps comprising reacting ammonia andethyl borate at a temperature above about 850 C., the'ammonia being pres ent in atleast a slight excess over a moleto moleratio with'ethyl borate, recovering the product 'of reaction, and passing ammonia over saidrecovered product of reaction at atemperature aboveaabout. 800 C.; to produce boron nitride. I

' 6'. A process forproducing boron nitride, .the steps comprising reacting ammonia and a.lower'a1kyl.b orate ester at a temperature above about850 C.,the ammonia I being present in at least a slight excess over amoleIto mole ratio with the borate ester, recovering the product of reaction, and passing ammonia-oversaid recovered product of reaction at a temperature above about 800 C. for several hours to produce boron nitride.

- 7. A process for producing boron nitride,

7 comprising reacting ammonia and methyl borate at;a

-tiallyfsimilar to the ones obtained on the white solid material prepared from the methyl borate-ammonia'vapor several hours to' produce boron nitride.

temperature above about 850 C'., the ammonia being a present in at least a slight excess over a mole-to mole a ratio with methyl borate, recovering the product of reac- 'tion, and passing ammonia oversaid'recovered product of reaction at a temperature above' about 800" C. for

8. A process for producing .boron nitride, the comprising reacting ammonia and ethyl borate at a temperature above about 850 C., the ammoniabeing; present ;in at least a slight excess over amole to mole ratio'with ethyl borate,recovering the product of reaction, and passing ammonia over said recovered product of reaction at a temperature abovepabout 800 C. for several hoursto produce boron nitride. V 1

9. A process for producing'boron nitride, the'steps comprising reacting ammonia and a lower alkyl borate ester at a temperature above about ;85 0 C., the ammonia being present in at least a slight excess over a mole to mole ratio with the borate ester," recovering the product of reaction, and passing ammoniapver said recovered product of reaction at a temperature above about-=800 850 C., the ammonia being present in at least aslight V excess over a mole to mole ratio with methyl borate, and recovering the product of reaction.

2. A process for producing boron nitride, the steps comprising reacting ammonia and-methyl borate at a temperature'above about 850 .C.', the ammonia being presentiinat-leastaslight excess 'over a mole to mole ratio with. methyl borate, recovering-the product of reaction, and passing ammoniaover-said recovered product of C. for several hours to produce boron nitride; c

, References Cited in the fileiof patent 'UNITEDSTATES PATENTS OTHER REFERENCES Finlay et al.: fBoron Nitride Unusual'Refractory, f American Ceramic Society Bulletin, vet-31, No; 4,pages Pease: Crystal Structurev of Boron Nitridefi" Chem:

Abstracts 44, 7116 (Nature l65'j 722-3 (1950));

Mellor: Treatise on Inorganic and"Theoretical Chemistry (1928), vol. 8, pages 108, 109

the steps tep 

1. IN A PROCESS FOR PRODUCING BORON NITRIDE THE STEPS OF PRODUCING A BORON COMPLEX COMPRISING REACTING AMMONIA AND METHYL BORATE AT A TEMPERATURE ABOVE ABOUT 850*C., THE AMMONIA BEING PRESENT IN AT LEAST A SLIGHT EXCESS OVER A MOLE TO MOLE RATIO WIGH METHYL BORATE, AND RECOVERING THE PRODUCT OF REACTION. 